/*-------------------------------------------------------------------------
 *
 * nodeResult.c--
 *    support for constant nodes needing special code.
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * DESCRIPTION	
 *
 *	Example: in constant queries where no relations are scanned,
 *	the planner generates result nodes.  Examples of such queries are:
 *
 *		retrieve (x = 1)
 *	and
 *		append emp (name = "mike", salary = 15000)
 *
 *	Result nodes are also used to optimise queries
 *	with tautological qualifications like:
 *
 *		retrieve (emp.all) where 2 > 1
 *
 *	In this case, the plan generated is
 *
 *			Result  (with 2 > 1 qual)
 *			/
 *		   SeqScan (emp.all)
 *
 * IDENTIFICATION
 *    $Header: /usr/local/cvsroot/postgres95/src/backend/executor/nodeResult.c,v 1.2 1996/10/31 10:12:18 scrappy Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"


#include "executor/executor.h"
#include "executor/nodeResult.h"

/* ----------------------------------------------------------------
 *   	ExecResult(node)
 *
 *	returns the tuples from the outer plan which satisify the
 *	qualification clause.  Since result nodes with right
 *	subtrees are never planned, we ignore the right subtree
 *	entirely (for now).. -cim 10/7/89
 *
 *   	The qualification containing only constant clauses are
 *   	checked first before any processing is done. It always returns
 *    	'nil' if the constant qualification is not satisfied.
 * ----------------------------------------------------------------
 */
TupleTableSlot *
ExecResult(Result *node)
{
    ResultState		*resstate;
    TupleTableSlot	*outerTupleSlot;
    TupleTableSlot	*resultSlot;
    Plan   		*outerPlan;
    ExprContext		*econtext;
    Node		*qual;
    bool		qualResult;
    bool		isDone;
    ProjectionInfo 	*projInfo;
    
    /* ----------------
     *	initialize the result node's state
     * ----------------
     */
    resstate =  node->resstate;
    
    /* ----------------
     *	get the expression context
     * ----------------
     */
    econtext = resstate->cstate.cs_ExprContext;
    
    /* ----------------
     *   check tautological qualifications like (2 > 1)
     * ----------------
     */
    qual = node->resconstantqual;
    if (qual != NULL) {
	qualResult = ExecQual((List*)qual, econtext);
	/* ----------------
	 *  if we failed the constant qual, then there
	 *  is no need to continue processing because regardless of
	 *  what happens, the constant qual will be false..
	 * ----------------
	 */
	if (qualResult == false)
	    return NULL;
	
	/* ----------------
	 *  our constant qualification succeeded so now we
	 *  throw away the qual because we know it will always
	 *  succeed.
	 * ----------------
	 */
	node->resconstantqual = NULL;
    }
    
    if (resstate->cstate.cs_TupFromTlist) {
	ProjectionInfo *projInfo;
	
	projInfo = resstate->cstate.cs_ProjInfo;
	resultSlot = ExecProject(projInfo, &isDone);
	if (!isDone)
	    return resultSlot;
    }

    /* ----------------
     *  retrieve a tuple that satisfy the qual from the outer plan until
     *  there are no more.
     *
     *  if rs_done is 1 then it means that we were asked to return
     *  a constant tuple and we alread did the last time ExecResult()
     *  was called, so now we are through.
     * ----------------
     */
    outerPlan = outerPlan(node);

    while (!resstate->rs_done) {

	/* ----------------
	 *    get next outer tuple if necessary.
	 * ----------------
	 */
	if (outerPlan != NULL) {
	    outerTupleSlot = ExecProcNode(outerPlan, (Plan*)node);
	
	    if (TupIsNull(outerTupleSlot))
		return NULL;
	    
	    resstate->cstate.cs_OuterTupleSlot = outerTupleSlot;
	} else {

	    /* ----------------
	     *  if we don't have an outer plan, then it's probably
	     *  the case that we are doing a retrieve or an append
	     *  with a constant target list, so we should only return
	     *  the constant tuple once or never if we fail the qual.
	     * ----------------
	     */
	    resstate->rs_done = 1;
	}
	
	/* ----------------
	 *    get the information to place into the expr context
	 * ----------------
	 */
	resstate =  node->resstate;
	
	outerTupleSlot = resstate->cstate.cs_OuterTupleSlot;
	
	/* ----------------
	 *   fill in the information in the expression context
	 *   XXX gross hack. use outer tuple as scan tuple
	 * ----------------
	 */
	econtext->ecxt_outertuple = outerTupleSlot;
	econtext->ecxt_scantuple =  outerTupleSlot;
	
	/* ----------------
	 *   form the result tuple and pass it back using ExecProject()
	 * ----------------
	 */
	projInfo = resstate->cstate.cs_ProjInfo;
	resultSlot = ExecProject(projInfo, &isDone);
	resstate->cstate.cs_TupFromTlist = !isDone;
	return resultSlot;
    }

    return NULL;
}

/* ----------------------------------------------------------------
 *   	ExecInitResult
 *   
 *   	Creates the run-time state information for the result node
 *   	produced by the planner and initailizes outer relations 
 *   	(child nodes).
 * ----------------------------------------------------------------
 */
bool
ExecInitResult(Result *node, EState *estate, Plan *parent)
{
    ResultState	    *resstate;
    
    /* ----------------
     *	assign execution state to node
     * ----------------
     */
    node->plan.state = estate;
    
    /* ----------------
     *	create new ResultState for node
     * ----------------
     */
    resstate = makeNode(ResultState);
    resstate->rs_done = 0;
    node->resstate = resstate;
    
    /* ----------------
     *  Miscellanious initialization
     *
     *	     +	assign node's base_id
     *       +	assign debugging hooks and
     *       +	create expression context for node
     * ----------------
     */
    ExecAssignNodeBaseInfo(estate, &resstate->cstate, parent);
    ExecAssignExprContext(estate, &resstate->cstate);
    
#define RESULT_NSLOTS 1
    /* ----------------
     *	tuple table initialization
     * ----------------
     */
    ExecInitResultTupleSlot(estate, &resstate->cstate);
    
    /* ----------------
     *	then initialize children
     * ----------------
     */
    ExecInitNode(outerPlan(node), estate, (Plan*)node);

    /*
     * we don't use inner plan
     */
    Assert(innerPlan(node)==NULL);
    
    /* ----------------
     * 	initialize tuple type and projection info
     * ----------------
     */
    ExecAssignResultTypeFromTL((Plan*)node, &resstate->cstate);
    ExecAssignProjectionInfo((Plan*)node, &resstate->cstate);
    
    /* ----------------
     *	set "are we done yet" to false
     * ----------------
     */
    resstate->rs_done = 0;
    
    return TRUE;
}

int
ExecCountSlotsResult(Result *node)
{
    return ExecCountSlotsNode(outerPlan(node)) + RESULT_NSLOTS;
}

/* ----------------------------------------------------------------
 *   	ExecEndResult
 *   
 *   	fees up storage allocated through C routines
 * ----------------------------------------------------------------
 */
void
ExecEndResult(Result *node)
{
    ResultState	    *resstate;
    
    resstate = node->resstate;
    
    /* ----------------
     *	Free the projection info
     *
     *  Note: we don't ExecFreeResultType(resstate) 
     *        because the rule manager depends on the tupType
     *	      returned by ExecMain().  So for now, this
     *	      is freed at end-transaction time.  -cim 6/2/91     
     * ----------------
     */    
    ExecFreeProjectionInfo(&resstate->cstate);
    
    /* ----------------
     *	shut down subplans
     * ----------------
     */
    ExecEndNode(outerPlan(node), (Plan*)node);

    /* ----------------
     *	clean out the tuple table
     * ----------------
     */
    ExecClearTuple(resstate->cstate.cs_ResultTupleSlot);
}
